A galvanic isolator provides a mean for moving a signal from one electrical circuit to another electrical circuit when the two electrical circuits must otherwise be electrically isolated from one another. Usually the two electrical circuits operate at different voltages, and thus, must be electrically isolated. For example, consider an application in which a 5V battery powered controller board is utilized to control a motor circuit operating at 240V. In this example, it is essential to electrically isolate the 240V motor circuits from the 5V controller circuit, while permitting the 5V controller circuit to send or receive signals from the 240V motor circuit. In this type of application, a galvanic isolator may be used to provide voltage and noise isolation, while permitting the information exchange between the two circuit systems. For electrical system with more than two circuits operating at different voltages, a multichannel galvanic isolator may be used.
There are three main types of galvanic isolators. The first type is a wireless radio frequency transceiver, in which a signal is sent from one circuit to another circuit via a wireless signal. The second type is a magnetic isolator in which the signal is transmitted from one circuit to another circuit by means of a magnetic field. The third type is an optocoupler in which the signal is transferred between circuits by means of light waves. Galvanic isolators may be used in applications involving voltage operating in kilovolts. Magnetic isolators and radio frequency isolators may have limitation in shielding noise from one circuit system to another circuit system because the entire circuit in the isolators may be susceptible to the strong magnetic field or the radio frequency waves that may induce voltage or current. However, optocouplers, couplings signals by means of light waves, do not induce noise in the same way that magnetic isolators or radio-frequency transceivers induce noise.
Generally, an optocoupler comprises an optical transmitter die and an optical receiver die. The optical transmitter die and the optical receiver die may be housed in a single package. A multichannel optocoupler may have more than one pair of optical transmitter or receiver dies. A signal is usually transmitted from the optical transmitter die to the optical receiver die. In order to prevent light loss, a light guide is typically employed. In most cases, the light guide is formed by dispensing a transparent encapsulant in liquid form over the optical transmitter and receiver dies. The transparent encapsulant is then hardened through a curing process into a light guide. The shape of the light guide may be dependent on the viscosity of the encapsulant, and therefore, the shape of the light guide may be difficult to control. This issue of controlling the light guide shape may be more severe for an optocoupler with large dies or for a multichannel optocoupler.